This week, we took a look at the difference just one Supreme Court Justice could make in one extraordinarily important abortion case – American College of Obstetricians & Gynecologists v. Food & Drug Administration. Today, we examine what legal sociologists (that is a thing) are saying about the magnitude of the Court’s potential ideological shift between the late Justice Ruth Bader Ginsburg and President Trump’s nominee for her seat, Judge Amy Coney Barrett of the Seventh Circuit Court of Appeals.

For those looking for objective measures of judicial philosophy, there is something called a “Martin-Quinn Score,” after the political scientists who ginned it up, Andrew D. Martin and Kevin M. Quinn. (Their paper on the genesis of the score is entitled “Dynamic Ideal Point Estimation via Markov Chain Monte Carlo for the U.S. Supreme Court, 1953–1999,” and since I’m not a qualitative sociologist, I didn’t read it. But here it is if you’re interested.) 

The big picture is that in the modern era, Republican presidents are all over Democrats in placing Justices on the Supreme Court, having elevated ten individuals to the High Court versus four for Democrats. Ronald Reagan put three new Justices on the bench – Sandra Day O’Connor, Antonin Scalia, and Anthony Kennedy. (Technically, he had five nominations, but one was his failed nomination of Robert Bork, for whom he substituted Kennedy, and Associate Justice William Rehnquist for Chief Justice.) After Reagan and until Donald Trump, the next four presidents have each had two, at a rate of roughly one every two and a half years. These include three presidents who had two nominations each over eight years: Bill Clinton (Stephen Breyer and Ruth Bader Ginsburg); George W. Bush (Samuel Alito and Chief Justice John Roberts); and Barack Obama (Elena Kagan and Sonia Sotomayor); and one  whose pair of picks spanned a single four-year term, George H.W. Bush (Clarence Thomas and David Souter). Obviously, that puts President Trump in singular company with his third nominee in his first term poised to gain a seat and join Neil Gorsuch and Brett Kavanaugh on the Court. Trump was speaking presciently when in one of the 2016 presidential debates he declared, “The Supreme Court is what’s it’s all about.”Historically, here’s what Supreme Court shifts in personnel have meant for the corporate ideological makeup of the Court, according to a graphing of all the Justices’ Martin-Quinn scores since the New Deal era.

Even setting uber-liberal Justice William O. Douglas aside as an outlier, it appears that there may be something to the perception that liberal justices take hard left turns more often than conservative ones take hard rights – witness Justices Brennan, Marshall, Stevens, Ginsburg, and Sotomayor among progressive-minded members of the Court, and Justices O’Connor, Roberts, and Kennedy on the right.

And in terms of ideological diversity, each nomination Trump has had has loomed larger. Justice Gorsuch replaced fellow conservative jurist Antonin Scalia, and by and large has mirrored his matter-of-fact textualist approach to judicial interpretation. Justice Kavanaugh, a pragmatic conservative, replaced a middling-conservative Justice, Anthony Kennedy, shifting the Court a bit to the Right.

Judge Barrett’s nomination could spell a much bigger shift for the Court. In fact, the political website thinks it could be the third biggest shift in the Court’s modern history, eclipsed only by Chief Justice Warren Burger’s replacement of Chief Justice Earl Warren in 1969, and Associate Justice Clarence Thomas’s replacement of Associate Justice Thurgood Marshall in 1991. Here’s how that looks on the graph of Martin-Quinn scores, according to FiveThirtyEight:

Considering the seismic magnitude of this impending shift, Trump may have played his cards well by nominating Brett Kavanaugh, a (politically) more vulnerable nominee, for Justice Kennedy’s seat and “saving Amy Barrett,” a much stronger candidate politically, for Justice Ginsburg’s seat, as he reportedly said.